This invention relates to optical printers, suitable for printing images and text on a print medium and, more particularly, to a printer wherein the print medium is moving in a first direction relative to a linear print head as the print head optically prints a line of print in a second direction perpendicular to the first direction. The printer includes an optical compensation element operative to progressively displace a line of print to negate any smear of the line resulting from the two directions of movement.
Printers are employed in a variety of applications, including the printing of documents and/or photographic images. In a common form of construction, the printer operates optically by exposing succeeding lines of print in a print medium. Typically, the line of print is a sequence of black and white marks on the print medium representing a portion of a line of alphanumeric characters or a line of pixels of an image. For example, in one type of printing apparatus, a linear light bar may extend across a photosensitive surface of the print medium in a direction perpendicular to the direction of movement of the medium to produce a line at each point of movement of the light bar relative to the medium. Thus, there is a two-dimensional scanning of the light bar across the print medium in the sense that the print medium is advancing in a first direction while the light bar extends across the medium in a second direction perpendicular to the first direction.
A problem arises in that, during a two-dimensional scanning of the print medium, the print medium continuously advances, even during the interval of time during which the light bar is exposing transversely across the medium, Therefore, the width of each exposed line becomes extended as a result of the continual advancement of the print medium, or page of print during line exposure, this resulting in a smearing of each print line and an overlap of succeeding adjacent lines. In the absence of some form of compensation for the smear, a resulting printed text or image is degraded.